Exhaust gases discharged from a diesel engine contain sulfate based on a sulfur content in fuel, tar-like particulate matter (referred to as “PM”) resulting from incomplete combustion, nitrogen oxides (NOx), and the like.
As a device for removing the PM contained in the exhaust gas of the diesel engine, an exhaust gas purification device for collecting the PM using a DPF and burning away the collected PM with proper timing is known.
Such a DPF is typically designed such that a porous filter substrate exhibiting a honeycomb structure makes up framework, and when the exhaust gas circulates inside a dividing wall of the substrate, the PM is collected in the surface of the dividing wall.
With respect to a catalyst for the exhaust gas of the diesel engine, for example, the following inventions are disclosed.
For example, a method of purifying an engine exhaust gas is disclosed in Patent Document 1 (JP 2003-286835 A), in which a granular or monolithic denitration catalyst and oxidation catalyst supporting titanium and silver on alumina are disposed in series on an exhaust passage of the engine exhaust gas, and the engine exhaust gas is brought into contact with the denitration catalyst under the presence of a fuel reducing agent extracting a part of fuel and is then brought into contact with the oxidation catalyst.
A structure is disclosed in Patent Document 2 (JP 2006-239544 A), in which a coating layer is formed on a surface of a porous inorganic substrate such as cordierite, the coating layer being formed of oxide particles such as alumina having pores composed of inter-particle gaps of 10 nm to 200 nm and pore-communicating holes of 10 nm or less through which the pores communicate with each other, and a catalyst component is supported into the pores in the coating layer.
An exhaust gas purification device is disclosed in Patent Document 3 (JP 2009-112962 A), which purifies an exhaust gas discharged from an internal combustion engine and includes a gas channel through which the exhaust gas circulates and a particulate filter that is provided in the gas channel and is formed with numerous pores, wherein an approximately entire introduction face of the particulate filter brought into contact with the exhaust gas is covered with a microporous material in which micropores having a smaller diameter than the pores are formed, and the microporous material includes a carrier composed of an oxide having oxygen storage/release capacity and a catalyst containing Ag supported on the carrier.
An exhaust gas purification device is disclosed in Patent Document 4 (JP 2009-85010 A), which purifies an exhaust gas discharged from an internal combustion engine and includes a can channel through which the exhaust gas circulates and a particulate filter (DPF) that is provided in the gas channel and is formed with numerous pores, wherein an approximately entire introduction face of the particulate filter brought into contact with the exhaust gas is covered with a microporous material in which micropores having a smaller diameter than the pores are formed.
An exhaust gas purification filter is disclosed in Patent Document 5 (JP 2011-218310 A) which includes: an inflow surface through which an exhaust gas containing a particulate matter flows; a discharge surface from which purified gas is discharged; and a filter substrate made of a porous body, wherein the filter substrate includes porous dividing walls and gas channels surrounded by the dividing walls, a porous film having a pore size smaller than a size of pores of the dividing walls is provided on each surface of the dividing walls, and microgrooves having a depth shallower than the thickness of the porous film are formed on at least a part of a surface of the porous film.